New measurement of the Sm144(α,γ)Gd148 reaction rate for the γ process
| Autor: | Hans Werner Becker, A. Blazhev, P. Scholz, P. Sprung, Carsten Münker, F. Heim, Andreas Zilges, Detlef Rogalla, Ulrich Giesen, V. Foteinou, Kai Zuber, H. Wilsenach |
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| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Physical Review C. 102 |
| ISSN: | 2469-9993 2469-9985 |
| Popis: | Background: Most of the heavier $p$ isotopes are believed to be produced in the $\ensuremath{\gamma}$ process whose reaction path crucially depends on the proton and $\ensuremath{\alpha}$-particle penetrability at sub-Coulomb energies. Both nuclei of the samarium $p$-process chronometer, $^{146}\mathrm{Sm}$ and $^{144}\mathrm{Sm}$, are produced in the $\ensuremath{\gamma}$ process, and their initial abundance ratio is very sensitive to the $(\ensuremath{\gamma},n)$ and $(\ensuremath{\gamma},\ensuremath{\alpha})$ branching ratio on $^{148}\mathrm{Gd}$. The $^{148}\mathrm{Gd}(\ensuremath{\gamma},\ensuremath{\alpha})^{144}\mathrm{Sm}$ reaction rate was measured roughly 20 years ago by means of the activation technique and its surprising results triggered adjustments to the global low-energy $\ensuremath{\alpha}+\text{nucleus}$ optical-model potentials (OMPs).Purpose: We want to take advantage of modern $\ensuremath{\alpha}$-particle spectroscopy techniques in order to constrain the controversial previous results on the $^{148}\mathrm{Gd}(\ensuremath{\gamma},\ensuremath{\alpha})^{144}\mathrm{Sm}$ reaction rate.Method: The $^{148}\mathrm{Gd}(\ensuremath{\gamma},\ensuremath{\alpha})^{144}\mathrm{Sm}$ reaction rate has been determined by measuring the cross section of the reverse reaction $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$, applying the activation technique to the $\ensuremath{\alpha}$ decay of $^{148}\mathrm{Gd}$. Targets have been irradiated at the cyclotron of the Physikalisch-Technische Bundesanstalt in Braunschweig, Germany. The $\ensuremath{\alpha}$-particle spectroscopy has been carried out with a state-of-the-art low-background ionization chamber of the Technische Universit\"at Dresden, Germany.Results: Cross sections for the $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$ reaction have been measured between 10.66 and 12.66 MeV with much higher precision than in the previous measurement. The results agree with earlier results within their uncertainties. The statistical-model analysis has been carried out using the talys code on the basis of the latest parametrizations of $\ensuremath{\alpha}$-OMPs. The best reproductions of the experimental results within the statistical model have been used to calculate the reaction rates.Conclusion: The values presented here suggest a steeper increase in the astrophysical $S$ factor towards lower center-of-mass energies. Different parametrizations of the $\ensuremath{\alpha}$-OMP were able to describe the experimental values sufficiently. Further measurements at energies below 11.0 MeV are suggested. |
| Databáze: | OpenAIRE |
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